Can't let this pass without providing the following link:
This page contains detailed instructions on how to disassemble a Kodak Brownie Hawkeye and clean the simple meniscus lens and the viewfinder optics. I did this to my Hawkeye and the optics now look like new.
Interestingly, using black photographic tape I also managed to mask off a portion of the opening in the simple rotary shutter to decrease my effective shutter speed. This sharpened up my negatives significantly from reduced hand shake.
In fact, I also measured and calculated the actual fixed lens aperture, added a filter factor for a #8 yellow filter, then used one of those Calumet shutter testers to help me mask off just the right amount of the shutter opening to give me perfect exposures (HP5+) when using that filter. Now I not only get nice clouds, but even more sharpness in my b&w negatives from the monochromatic subject light.